1. Field of the Invention
This invention concerns energy delivery system and method for a gate drive unit controlling a thyristor-based valve. it relates notably to FACTS (Flexible AC Transmission System). The field of the invention is the field of power electronics related to the thyristor-based valve design.
2. Description of the Related Art
In such a field, both HVDC (“High Voltage Direct Current”) and FACTS use power electronic converters for the power conversion and power quality control. High power thyristors have been serving as the key component in HVDC and FACTS converters for several decades now and are still being further developed for higher power rating nowadays. Many thyristors connected in series together with specially designed auxiliary mechanical and electronic systems build so called thyristor valves, which forms the HVDC and FACTS converters.
FACTS thyristor valves serve industrial and utility markets. Such applications may require two different branch topologies: TCR (Thyristor Controlled Reactor) and TSC (Thyristor Switched Capacitor). Due to the switching (turn on and turn off) principles, TCR and TSC topologies may require different energy delivery systems to each one of the gate drive units on each thyristor level. Following are the key methods of providing energy or power to the gate drive units:                from main power circuit:                    a. a method using the voltage across damping/grading circuits during thyristor off-state with snubber pickup methodology;            b. a method using the current in the main power circuit via a current transformer exposed to a bidirectional AC current waveform;                        from the ground level:                    a. a method accomplished magnetically via a high voltage isolating transformer, as shown in FIG. 1;            b. an optical method via a laser and a fiber.                        
As shown in FIG. 1, a known ground level power supply methodology illustrates an energy delivery system comprising the following elements:                thyristors 10, with gate drive units 11,        two induction coils 14,        a ground level based inverter 13 (Ground Level Power Supply or GLPS),        a high voltage isolating transformer 12.        
These two last elements 12 and 13 carry following deficiencies:                They are very bulky in size, thus adding to the overall size of the valve and then forcing large sizes of the valve hall. A ground level based inverter is bulky, complex and designed with the necessary voltage unreliable solution. Production of such an equipment is costly and requires significant real estate space in the valve hall. In addition usually the ground level power supply system is located on the floor level in close proximity to the thyristor valve. Any significant coolant leaks will cause shutdown of the specific thyristor branch.        They are key elements reflecting on the overall reliability and availability of the SVC (Static VAR compensator) system. In order to achieve desired reliability and longevity, they are designed with a high level of the rating margins. This fact reflects directly on their very high production costs, and need for the maintenance.        The inverter 13 as being active device which directly effects reliability of the system, is designed with the very costly magnetic components, thus further elevating the costs of the entire system.        
So such a current energy delivery system for a gate drive unit controlling a thyristor-based valve, is expensive, difficult to manufacture and to test.
The purpose of the invention is to provide an energy delivery system for a gate drive unit controlling a thyristor-based valve which eliminates the above drawbacks.